staging: wilc1000: fix freeing of ERR_PTR

If memdup_user() fails then it will return the error code in ERR_PTR. We
were checking it with IS_ERR but then again trying to free it on the
error path.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>